In an optical encoder module, the emitter and the detector have to be spaced apart from each other and aligned to each other such that, for example, a code card or a code wheel drawn or rotated, respectively, in a gap between the emitter and the detector can be detected and read by the encoder. Light emitted by the emitter is either blocked or passed by the code card or wheel and then detected by the detector. Therefore, it is important that the emitter and the detector are exactly aligned to each other, i.e. the emitter and the detector have to accurately overlap each other.
U.S. Design Pat. No. 329,193 discloses an optical encoder module having an optical emitter and an optical detector, the emitter and the detector being each provided with a solid molded housing, wherein both the emitter and detector housings are held together by means of a bracket. The bracket has a locking plate including a locking opening. The optical encoder module (i.e. one of the housings) has a locking protrusion that engages with the locking opening of the locking plate. Ribs are formed inside the bracket, and the emitter and detector housings are provided with laterally elongated grooves for receiving the ribs of the bracket.
However, since the emitter and detector housings can be manufactured with certain tolerance values and therefore with some accuracy only, once the respective housings are held together with the bracket, the emitter and the detector can be offset relative to each other resulting in deterioration of the detecting operation. This problem can further be deteriorated by mechanical inaccuracy of the bracket and an inaccurate engagement of the ribs of the bracket with the elongated grooves in the emitter and detector housings.
Other known arrangements do not mold the emitter and detector components in respective housings. In this case, the emitter and detector components are only provided with a simple encapsulation and are mechanically inserted into separately manufactured housings.
Inserting components inside a housing is a well-known operation in many assembly processes. In many cases, the components need to be fitted tightly and snugly inside the housing such that they maintain their positional orientations vital to the functioning of the completely mounted assembly. However, the dimensions of the components as well as the housings are subject to fabrication tolerances that cause the components to have slightly different dimensions. Because of these dimensional variations, matching problems may arise when the components and the housing or housings are mounted into an assembly.
In the assembly process where components are being inserted into respective recesses of a housing, it is important that the tolerances of both the components and the recesses are compatible. For perfect matching, the dimensions of, e.g the length of the recess should be equal to the dimensions, e.g. the length of the component. However, there are tolerances in both of these dimensions. When the length of the component is at maximum dimension and the length of the recess is at minimum dimension, it may even happen that the component cannot be inserted into the housing. Conversely, when the length of the component is at minimum dimension and the length of the recess is at maximum dimension, the component will be too loose after insertion into the housing.
In order to ensure that all components be inserted into the housing, the tolerances are typically specified such that the maximum dimension of the component is equal to the minimum dimension of the respective recess in the housing. In this case, a mismatch of the component and the housing is prevented.
Furthermore, in order to ensure an accurate positional orientation of the component in the respective housing, generally glue, adhesive, a clip or a plug is used to secure the component in the housing. In other cases, after insertion of the electrical component into the housing, the housing is deformed through heat staking such that the component is jammed tight inside the housing. In other instances, a mechanical catch or latch is used. Yet in other cases, the component is sized such that there is mechanical interference between the component and the corresponding recess during the component insertion process.
Such methods are successflly used in the industry but they suffer from limitations. Glue, adhesive, plugs or clips represent additional materials that naturally incur extra costs. In addition, an extra process step is needed to handle these materials prior to or after component insertion. This makes the assembly process more complicated and increases the cost of manufacturing. In some cases mechanical catches or latches cannot be applied because it is very difficult or even impossible to make them, and mechanical interference can lead to deformation of the housing, and thereby to the formation of cracks in the housing and/or the components.